A plant monitoring apparatus that performs monitoring of a power generation plant, a chemical plant, or the like includes many functions for monitoring the plant. Examples of such functions include a warning monitoring function and a graph display function. The warning monitoring function is, for example, a function for notifying an operator that the plant falls into a warning state.
As a method of notifying a warning, for example, there is a method of displaying warning messages in time series as a list on a warning screen 18 illustrated in FIG. 27 to notify the warning to the operator. In this case, the operator checks a change in a process value obtained from a point, where the plant falls into the warning state, to check a state of a monitoring target in which the point is arranged. For example, a graph screen 19 on which a process value is displayed in time series illustrated in FIG. 28 is displayed on a display device using the graph display function.
However, on the graph screen 19 in the past, only a process value set as a monitoring target is displayed. For example, FIG. 29 shows a time-series change of a process value 290 after the plant falls into the warning state. When such a time-series change of the process value 290 is displayed on the graph screen 19 in the past, the time-series change after the plant falls into the warning state (a star mark) is a substantially fixed value. Therefore, the warning state does not seem to be worsening.
However, since a process value 291 used for calculation of a limit value corresponding to the process value 290 gradually decreases, a value of the limit value also gradually decreases. Therefore, a difference between the limit value and the process value 290 gradually increases. The plant is changing to a dangerous state. In this way, it is sometimes difficult to grasp a tendency of the state change of the monitoring target, that is, whether the state of the plant is worsening or improving according to the elapse of time.
In the graph display function in the past, for example, since display processing of the graph is performed using a screen different from the warning screen, the processing is complicated. For example, the graph cannot be immediately displayed from the warning screen.